Numerically-controlled in situ milling machines are known in the prior art for providing automated milling processes. Numerically-controlled milling machines are sometimes used for machining compressor parts of gas turbine engines such as fan blades, integrally bladed rotors or impellers, for example from a solid forging. Up to 90% of the mass of the solid forging is removed after long machining operations. Machining of long blades requires long tools to be used in all operations including roughing, semi-finishing and finishing. The tools deflect during machining operation due to their low bending stiffness and do not remove exact amounts of material as programmed. Cutting forces are proportional to the tool-and-part engagement conditions, which continuously change throughout a machining process of airfoils in five-degree-freedom operation such that the deflection of the tools and therefore remaining material on the blade surfaces, vary in every operation and for each individual blade. Dimensional variations within accepted tolerance ranges caused by eccentricity of the tool, holder and spindle and unbalance asymmetries in the tool shape, can further contribute to variations in tool engagement and deflection. All these factors lead to dimensional variations and a potentially significant mismatch between the machined section of the blades, which require extensive re-working after the machining process is completed. Re-working is a manual process and may cause dimensional deviations on the blades which affect the performance thereof
Accordingly, there is a need to provide an improved numerically-controlled machining operation.